Creating in-via routing with a light pipe

ABSTRACT

Creating in-via routing with a light pipe is disclosed. A resist layer is applied over a layer of conductive material provided in a via. A light pipe is inserted into the via. The surface of the light pipe includes at least one masked portion and at least one unmasked portion. A portion of the resist layer is exposed with light emitted from the unmasked portions of the light pipe. Portions of the conductive layer corresponding to the exposed portion of the resist layer are then removed to create the in-via routing.

BACKGROUND Field of the Invention

The field of the invention relates to conductive vias in printed circuitboards, or, more specifically, methods, apparatus, and products forcreating in-via routing with a light pipe.

Description Of Related Art

The development of the EDVAC computer system of 1948 is often cited asthe beginning of the computer era. Since that time, computer systemshave evolved into extremely complicated devices. Today's computers aremuch more sophisticated than early systems such as the EDVAC. Computersystems typically include a combination of hardware and softwarecomponents, application programs, operating systems, processors, buses,memory, input/output devices, and so on. As advances in semiconductorprocessing and computer architecture push the performance of thecomputer higher and higher, more sophisticated computer software hasevolved to take advantage of the higher performance of the hardware,resulting in computer systems today that are much more powerful thanjust a few years ago.

As computer systems become more complex, there is an ever-growing needto fabricate complex electrical circuits while minimizing the spaceoccupied by electrical components. To that end, circuits fabricated onprinted circuit boards frequently consist of multiple electrical tracesdistributed over multiple layers, or planes, of the printed circuitboard (PCB). Electrical traces on surfaces and different interior planesof the PCB may be electrically connected with a plated through hole, orplated via. A via is a hole in a PCB that may be plated withelectrically conductive material on its sides so that two or more tracesintersecting the via may be electrically connected.

PCB vias are typically constructed to electrically connect signals todifferent planes of the printed circuit board. There are instances wherea single via location could connect more than one electrical signal.Although there are methods for splitting vias through mechanical means,these vias are typically split in the X or Y direction. Typically, viastransfer only single function, whether power or a signal, in Z directionof the PCB. Furthermore, for various reasons such as time, cost, orcomplexity, it is desirable to avoid mechanical processing to achieve asplit via.

SUMMARY

Embodiments of the present invention provide the ability to split a viathe Z direction without the need for post-plating mechanical processingof the via using light pipe technology. By splitting the via in the Zdirection, multiple signals may be transferred in the Z direction of thePCB thereby providing more space efficiency in circuit design andimplementation.

An embodiment in the present disclosure is directed to a method ofcreating in-via routing with a light pipe, the method comprisingapplying a resist layer over a layer of conductive material provided ina via, inserting the light pipe into the via, wherein the surface of thelight pipe includes at least one masked portion and at least oneunmasked portion, exposing a portion of the resist layer with lightemitted from the at least one unmasked portion of the light pipe, andremoving a portion of the conductive layer corresponding to the exposedportion of the resist layer.

Another embodiment in the present disclosure is directed to a system forcreating in-via routing with a light pipe, the apparatus comprising, alight pipe, wherein the surface of the light pipe includes at least onemasked portion and at least one unmasked portion, a light source, and avia in which is disposed a layer of conductive material, wherein thesystem is configured to carry out the steps of: applying a resist layerover the layer of conductive material provided in a via, inserting thelight pipe into the via, exposing a portion of the resist layer withlight emitted from the at least one unmasked portion of the light pipe,and removing a portion of the conductive layer corresponding to theexposed portion of the resist layer.

Yet another embodiment in the present disclosure is directed to amultilayer printed circuit board comprising at least two conductivetraces, at least one insulator layer separating the at least twoconductive traces, and at least one via in a direction perpendicular toa plane of the printed circuit board that intersects the at least twoconductive traces, wherein the at least one via is configured within-via routing, wherein the in-via routing is form by: applying a resistlayer over a layer of conductive material provided in the via, insertingthe light pipe into the via, exposing a portion of the resist layer withlight emitted from the at least one unmasked portion of the light pipe,and removing a portion of the conductive layer corresponding to theexposed portion of the resist layer.

In some embodiments, applying a resist layer over a layer of conductivematerial provided in a via includes providing the via, wherein the viahas been plated with the conductive material. In further embodiments,removing a portion of the conductive layer corresponding to the exposedportion of the resist layer includes etching the via with acid. Invarious embodiments, the resist layer is a positive photoresistmaterial. In still further embodiments, removing a portion of theconductive layer corresponding to the exposed portion of the resistlayer creating at least two independent connections between in the via.In still further embodiments, further plating of the via with additionalconductive material is omitted. In yet a further embodiment, furtherdrilling of the via is omitted.

In still further embodiments, removing a portion of the conductive layercorresponding to the exposed portion of the resist layer includesremoving a conductive stub between a conductive pad on a surface of theprinted circuit board and a conductive trace in an interior layer of theprinted circuit board. Removing a portion of the conductive layercorresponding to the exposed portion of the resist layer may alsoinclude removing partially removing conductive material between a firstconductor in a first interior layer of the printed circuit board and asecond conductor in a second interior layer of the circuit board.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a cross-section view of an exemplaryprinted circuit board;

FIG. 2 is a diagram illustrating a 3-dimensional view of an exemplaryvia;

FIG. 3 is a diagram illustrating a system for creating in-via routingwith a light pipe according to embodiments of the present invention;

FIG. 4 is a flow chart illustrating a method for creating in-via routingwith a light pipe according to embodiments of the present invention;

FIG. 5 is a flow chart illustrating a method for creating in-via routingwith a light pipe according to embodiments of the present invention;

FIG. 6 is a flow chart illustrating a method for creating in-via routingwith a light pipe according to embodiments of the present invention;

FIG. 7 is a flow chart illustrating a method for creating in-via routingwith a light pipe according to embodiments of the present invention;

FIG. 8 is a diagram illustrating a cross-sectional view of creating atestable split via by in-via routing with a light pipe according toembodiments of the present invention;

FIG. 9 is a diagram illustrating a cross-sectional view of creating atestable split via by in-via routing with a light pipe according toembodiments of the present invention;

FIG. 10 is a diagram illustrating a cross-sectional view of a testablesplit via created by in-via routing with a light pipe according toembodiments of the present invention;

FIG. 11 is a diagram illustrating a 3-dimensional view of a testablesplit via created by in-via routing with a light pipe according toembodiments of the present invention;

FIG. 12 is a diagram illustrating a masked light pipe for creatingin-via routing according to embodiments of the present invention;

FIG. 13 is a diagram illustrating a cross-sectional view of the creationof an untestable split via by in-via routing with a light pipe accordingto embodiments of the present invention;

FIG. 14 is a diagram illustrating a cross-sectional view of anuntestable split via created by in-via routing with a light pipeaccording to embodiments of the present invention;

FIG. 15 is a diagram illustrating a 3-dimensional view of an untestablesplit via created by in-via routing with a light pipe according toembodiments of the present invention;

FIG. 16 is a diagram illustrating a masked light pipe for creatingin-via routing according to embodiments of the present invention;

FIG. 17 is a diagram illustrating a 3-dimensional view of a via withnon-adjacent in-via routing created with a light pipe according toembodiments of the present invention;

FIG. 18 is a diagram illustrating a masked light pipe for creatingin-via routing according to embodiments of the present invention;

FIG. 19 is a diagram illustrating a 3-dimensional view of a via withnon-adjacent in-via routing created with a light pipe according toembodiments of the present invention;

FIG. 20 is a diagram illustrating a masked light pipe for creatingin-via routing according to embodiments of the present invention; and

FIG. 21 is a diagram illustrating a 3-dimensional view of a via within-via routing of differential traces created with a light pipeaccording to embodiments of the present invention.

DETAILED DESCRIPTION

Exemplary methods, apparatus, and products for creating in-via routingwith a light pipe in accordance with the present invention are describedwith reference to the accompanying drawings, beginning with FIG. 1. FIG.1 sets forth a cross-sectional via of an exemplary multilayer printedcircuit board (PCB) (115) configured for creating in-via routing with alight pipe according to embodiments of the present invention. Themultilayer PCB (115) of FIG. 1 includes a via (105) that is a drilledthrough-hole from an annular conductive pad (118) on a top exposedsurface (116) to an annular conductive pad (119) on a bottom exposedsurface (117). The top surface (116) and bottom surface (117) of the PCBmay have formed thereon conductive traces connecting to the conductivepads (118, 119). The interior of the PCB (115) includes wiring planes inwhich the electrically conductive traces (132 a, 132 b, 132 c, 132 d)are formed, and which are separated by insulating layers (122 a, 122 b,122 c, 122 d, 122 e) comprised of an insulating material. Via (105)intersects the traces (132 a, 132 b, 132 c, 132 d) and is lined with aconductive material (140) thereby forming a conductive conduit that mayconnect some or all of the traces (132 a, 132 b, 132 c, 132 d). In someembodiments of the present disclosure, the conductive material iscopper. The arrangement and quantity of the interior traces (132 a, 132b, 132 c, 132 d) and insulating layers (122 a, 122 b, 122 c, 122 d, 122e) in the PCB (115) illustrated in FIG. 1 are for explanation, not forlimitation.

For further explanation, FIG. 2 illustrates an exemplarythree-dimensional view of via (105) in which the insulating layers (122a, 122 b, 122 c, 122 d, 122 e) shown in FIG. 1 are omitted for clarity.FIG. 2 shows the via (105), as depicted in FIG. 1, intersecting theinterior traces (132 a, 132 b, 132 c, 132 d) at circular pad sections,which are electrically connected by the conductive material (140).

FIG. 3 illustrates a system (100) configured for creating in-via routingwith a light pipe according to embodiments of the present invention.FIG. 3 continues the example illustrated in FIG. 1 in that FIG. 3 alsoincludes the via (105) that is a drilled through-hole from an annularconductive pad (118) on a top exposed surface (116) to an annularconductive pad (119) on a bottom exposed surface (117). The top surface(116) and bottom surface (117) of the PCB may have formed thereonconductive traces connecting to the conductive pads (118, 119). Theinterior of the PCB (115) includes wiring planes in which theelectrically conductive traces (132 a, 132 b, 132 c, 132 d) are formed,and which are separated by insulating layers (122 a, 122 b, 122 c, 122d, 122 e) comprised of an insulating material. Via (105) intersects thetraces (132 a, 132 b, 132 c, 132 d) and is lined with a conductivematerial (140) thereby forming a conductive conduit that may connectsome or all of the traces (132 a, 132 b, 132 c, 132 d). In addition, aresist layer (150) is applied to the surface of the conductive material(140) in the via (105). In some embodiments of the present disclosure,the resist layer (150) is comprised of a positive photoresist materialthat is degraded by exposure to light.

Further, the system of FIG. 3 includes a masked light pipe (110) (notdrawn to scale) coupled to a light source (190) capable of transmittinghigh energy light through the light pipe (110). The light pipe (110)includes a masked portion (112), which is opaque to inhibit the passageof light, and unmasked portion (111) through which light is freelytransmitted from the light pipe. The light source (190) may be, forexample, a laser. Although not drawn to scale, it may be ascertainedfrom FIG. 3 that the light pipe may be inserted into the via (105).

Further, the system of FIG. 3 includes a sensor light source (192) andsensor detector that are perpendicular to the light pipe (110). When thelight pipe (110) is inserted into the via (105), light from the sensorlight source (192) passes through an unmasked region (193) of the lightpipe and is detected by the sensor detector (191) to ascertain the exactposition X, Y, and Z position of the light pipe (110) in the via (105).That is, the yaw, tilt, and pitch of the light pipe (110) within the via(105) may be controlled through feedback from the sensor detector (191),for example, by a mechanical controller (not shown).

For further explanation, FIG. 4 sets forth a flow chart illustrating anexemplary method for creating in-via routing with a light pipe accordingto embodiments of the present invention that includes applying a resistlayer over a layer of conductive material provided in a via (410),inserting the light pipe into the via, wherein the surface of the lightpipe includes at least one masked portion and at least one unmaskedportion (420), exposing a portion of the resist layer with light emittedfrom the at least one unmasked portion of the light pipe (430), andremoving a portion of the conductive layer corresponding to the exposedportion of the resist layer (440).

For further explanation, FIG. 5 sets forth a flow chart illustrating anexemplary method for creating in-via routing with a light pipe accordingto embodiments of the present invention FIG. 5 is similar to FIG. 4 inthat it includes applying a resist layer over a layer of conductivematerial provided in a via (410), inserting the light pipe into the via,wherein the surface of the light pipe includes at least one maskedportion and at least one unmasked portion (420), exposing a portion ofthe resist layer with light emitted from the at least one unmaskedportion of the light pipe (430), and removing a portion of theconductive layer corresponding to the exposed portion of the resistlayer (440).

In the example of FIG. 5, removing a portion of the conductive layercorresponding to the exposed portion of the resist layer (440)additionally includes etching (510) the via with acid or the like toremove the copper that lies underneath the exposed portions of theresist layer.

For further explanation, FIG. 6 sets forth a flow chart illustrating anexemplary method for creating in-via routing with a light pipe accordingto embodiments of the present invention FIG. 6 is similar to FIG. 4 inthat it includes applying a resist layer over a layer of conductivematerial provided in a via (410), inserting the light pipe into the via,wherein the surface of the light pipe includes at least one maskedportion and at least one unmasked portion (420), exposing a portion ofthe resist layer with light emitted from the at least one unmaskedportion of the light pipe (430), and removing a portion of theconductive layer corresponding to the exposed portion of the resistlayer (440).

In the example of FIG. 6, removing a portion of the conductive layercorresponding to the exposed portion of the resist layer (440)additionally includes creating at least two independent connectionsbetween in the via (610) by removal of the intervening conductivematerial.

For further explanation, FIG. 7 sets forth a flow chart illustrating anexemplary method for creating in-via routing with a light pipe accordingto embodiments of the present invention FIG. 7 is similar to FIG. 4 inthat it includes applying a resist layer over a layer of conductivematerial provided in a via (410), inserting the light pipe into the via,wherein the surface of the light pipe includes at least one maskedportion and at least one unmasked portion (420), exposing a portion ofthe resist layer with light emitted from the at least one unmaskedportion of the light pipe (430), and removing a portion of theconductive layer corresponding to the exposed portion of the resistlayer (440).

In the example of FIG. 7, removing a portion of the conductive layercorresponding to the exposed portion of the resist layer (440)additionally includes omitting any further plating of the via (710)and/or omitting any further mechanical processing of the via (720) suchas back-drilling. Additional plating and/or back-drilling of the via maybe omitted by virtue of the light pipe technology used to create thein-via routing.

For further explanation, FIG. 8 sets forth a diagram illustrating afurther exemplary system for creating in-via routing with a light pipeaccording to embodiments of the present invention. Continuing theexample shown in FIG. 3, FIG. 8 includes the PCB (115), the light pipe(110), and the light source (190), which are not drawn to scale in FIG.8. Via (105) is a drilled through-hole from an annular conductive pad(118) on a top exposed surface (116) to an annular conductive pad (119)on a bottom exposed surface (117). The top surface (116) and bottomsurface (117) of the PCB may have formed thereon conductive tracesconnecting to the conductive pads (118, 119). The interior of the PCB(115) includes wiring planes in which the electrically conductive traces(132 a, 132 b, 132 c, 132 d) are formed, and which are separated byinsulating layers (122 a, 122 b, 122 c, 122 d, 122 e) comprised of aninsulating material. Via (105) intersects the traces (132 a, 132 b, 132c, 132 d) and is lined with a conductive material (140) thereby forminga conductive conduit that may connect some or all of the traces (132 a,132 b, 132 c, 132 d). The resist layer (150) is applied to the surfaceof the conductive material (140) in the via (105). In the example ofFIG. 8, insertion (420) of the light pipe (110) into the via (105) isillustrated.

Further, the system of FIG. 8 includes a sensor light source (192) andsensor detector that are perpendicular to the light pipe (110). When thelight pipe (110) is inserted into the via (105), light from the sensorlight source (192) passes through an unmasked region (193) of the lightpipe and is detected by the sensor detector (191) to ascertain the exactposition X, Y, and Z position of the light pipe (110) in the via (105).That is, the yaw, tilt, and pitch of the light pipe (110) within thelight pipe may be controlled through feedback from the sensor detector(191), for example, by a mechanical controller (not shown).

For further explanation, FIG. 9 sets forth a diagram illustrating afurther exemplary system for creating in-via routing with a light pipeaccording to embodiments of the present invention. Continuing theexample shown in FIG. 8, FIG. 9 illustrates exposure (430) portions ofthe resist layer (151) to high energy light transmitted from theunmasked portions (112) of the light pipe (110) from activation of thelight source (190).

For further explanation, FIG. 10 sets forth a diagram illustrating afurther exemplary system for creating in-via routing with a light pipeaccording to embodiments of the present invention. Continuing theexample shown in FIG. 9, FIG. 10 illustrates the removal (440) of theconductive material (140) corresponding to the exposed portions (151) ofthe resist layer. In some embodiments of the present disclosure, theremoval (440) of the conductive material (140) may be an etching process(510) from the application of acid to the via (105). After the removal(440) of the conductive material (140), it can be seen that an electricconnection (1010) is made between the top (116) of PCB (115), theconductive trace A (132 a), and the conductive trace B (132 b) through afirst portion of the remaining conductive material (140). A second andindependent electrical connection (1020) is made between the bottom(117) of PCB (115), conductive trace C (132 c), and conductive trace D(132 d) through a second remaining portion of the conductive material.

For further explanation, continuing the example of FIG. 10, FIG. 11 setsforth an exemplary diagram illustrating a three-dimensional perspectiveview of the in-via routing achieved in the example of FIG. 10 by theindependent electrical connections (1010, 1020). In the example of FIG.11, traces (132 a, 132 b, 132 c, 132 d) are shown with the insulatinglayers (122 a, 122 b, 122 c, 122 d, 122 e) omitted for clarity. In theexample of FIG. 11, the connections (1010, 1020) are testable from theconductive pads (118, 119) respectively. Stubs of conductive materialconnecting the top pad (118) to trace A (132 a) and the bottom pad (119)to trace D (132 d) have not been removed, thus certain parasitic factorscaused by that material may exist.

FIG. 12 illustrates a masked light pipe (210) (not drawn to scale) inaccordance with another embodiment of the present disclosure. As in theexample of FIG. 3, the masked light pipe (210) includes a masked portion(111), which is opaque to inhibit the passage of light, and unmaskedportion (112) through which light from light source (190) is freelytransmitted from the light pipe. Masked light pipe (210) furtherincludes an unmasked region (193) for use with the position detectionsensors previously described.

For further explanation, FIG. 13 is a diagram illustrating a furtherexemplary system for creating in-via routing with a light pipe accordingto embodiments of the present invention. Continuing the example in FIG.8 using the light pipe (210) of FIG. 12, FIG. 13 illustrates insertion(420) of the light pipe (210) of FIG. 12 into the via (105), andexposure (430) of portions the resist layer (1351) to high energy lighttransmitted from the unmasked portions (112) of the light pipe (210)from activation of the light source (190).

Further, the system of FIG. 13 includes a sensor light source (192) andsensor detector that are perpendicular to the light pipe (110). When thelight pipe (110) is inserted into the via (105), light from the sensorlight source (192) passes through an unmasked region (193) of the lightpipe and is detected by the sensor detector (191) to ascertain the exactposition X, Y, and Z position of the light pipe (110) in the via (105).That is, the yaw, tilt, and pitch of the light pipe (110) within thelight pipe may be controlled through feedback from the sensor detector(191), for example, by a mechanical controller (not shown).

For further explanation, FIG. 14 sets forth a diagram illustrating afurther exemplary system for creating in-via routing with a light pipeaccording to embodiments of the present invention. Continuing theexample shown in FIG. 13, FIG. 14 illustrates the removal (440) of theconductive material (140) corresponding to the exposed portions (1351)of the resist layer. After the removal (440) of the conductive material(140), it can be seen that an electric connection (1410) is made theconductive trace A (132 a), and the conductive trace B (132 b) through afirst portion of the remaining conductive material (140). A second andindependent electrical connection (1420) is made between conductivetrace C (132 c), and conductive trace D (132 d) through a secondremaining portion of the conductive material (140). The resulting in-viarouting created by the independent connections (1410, 1420) is blind inthat it cannot be tested from the top and bottom surfaces (116, 117) ofthe PCB (115) by conductive pads (118, 119).

For further explanation, continuing the example of FIG. 14, FIG. 15 setsforth an exemplary diagram illustrating a three-dimensional perspectiveview of the in-via routing achieved in the example of FIG. 14 by theindependent electrical connections (1410, 1420). In the example of FIG.15, traces (132 a, 132 b, 132 c, 132 d) are shown with the insulatinglayers (122 a, 122 b, 122 c, 122 d, 122 e) omitted for clarity. In theexample of FIG. 11, the connections (1410, 1420) are not testable fromthe conductive pads (118, 119) respectively. Stubs of conductivematerial connecting the top pad (118) to trace A (132 a) and the bottompad (119) to trace D (132 d) have been removed, thus eliminatingparasitic factors caused by that material.

FIG. 16 illustrates a masked light pipe (310) (not drawn to scale) inaccordance with another embodiment of the present disclosure. As in theexample of FIG. 3, the masked light pipe (310) includes masked portions(111), which are opaque to inhibit the passage of light, and unmaskedportions (112) through which light from light source (190) is freelytransmitted from the light pipe. Masked light pipe (310) furtherincludes an unmasked region (193) for use with the position detectionsensors previously described.

For further explanation, FIG. 17 sets forth an exemplary diagramillustrating a three-dimensional perspective view of the in-via routingachieved in using the light pipe (310) of FIG. 16 by independentelectrical connections (1710, 1720). In the example of FIG. 17, traces(132 a, 132 b, 132 c, 132 d) are shown with the insulating layers (122a, 122 b, 122 c, 122 d, 122 e) omitted for clarity. The conductivetraces C and B (132 b, 132 c) do not fully surround the via (105), thusallowing the first independent connection (1710) between non-adjacenttraces A and D (132 a, 132 d), and a second independent connection(1720) between adjacent traces B and C (132 b, 132 c). Stubs ofconductive material connecting the top pad (118) to trace A (132 a) andthe bottom pad (119) to trace D (132 d) have been removed, thuseliminating parasitic factors caused by that material. The additionalremoval of conductive material from the sidewalls of the via (105)further reduces parasitics in the via.

FIG. 18 illustrates a masked light pipe (410) (not drawn to scale) inaccordance with another embodiment of the present disclosure. As in theexample of FIG. 3, the masked light pipe (410) includes masked portions(111), which are opaque to inhibit the passage of light, and unmaskedportions (112) through which light from light source (190) is freelytransmitted from the light pipe. Masked light pipe (410) furtherincludes an unmasked region (193) for use with the position detectionsensors previously described.

For further explanation, FIG. 19 sets forth an exemplary diagramillustrating a three-dimensional perspective view of the in-via routingachieved in using the light pipe (310) of FIG. 16 by independentelectrical connections (1910, 1920). In the example of FIG. 19, traces(132 a, 132 b, 132 c, 132 d) are shown with the insulating layers (122a, 122 b, 122 c, 122 d, 122 e) omitted for clarity. The conductivetraces C and B (132 b, 132 c) do not fully surround the via (105), thusallowing the first independent connection (1910) between non-adjacenttraces A and C (132 a, 132 c), and a second independent connection(1920) between adjacent traces B and D (132 b, 132 d).

FIG. 20 illustrates a masked light pipe (510) (not drawn to scale) inaccordance with another embodiment of the present disclosure. As in theexample of FIG. 3, the masked light pipe (510) includes masked portions(111), which are opaque to inhibit the passage of light, and unmaskedportions (112) through which light from light source (190) is freelytransmitted from the light pipe. Masked light pipe (510) furtherincludes an unmasked region (193) for use with the position detectionsensors previously described.

For further explanation, FIG. 21 sets forth an exemplary diagramillustrating a three-dimensional perspective view of the in-via routingachieved in using the light pipe (510) of FIG. 20. It will be recognizedthat the perspective view of FIG. 21 is rotated 90 degrees relative tothe view in FIG. 20. In the example of FIG. 21, differential pairs oftraces are shown. The wiring layers in the PCB include a firstdifferential pair A+ and A− (431 a, 431 b), a second differential pairB+ and B− (432 a, 432 b), a third differential pair C+ and C− (433 a,433 b), and a fourth differential pair D+ and D− (434 a, 434 b). In theexample of FIG. 21, first differential pair A+ and A− (431 a, 431 b) andsecond differential pair B+ and B− (432 a, 432 b) are connected by adifferential connection (2110 a, 2210 b). Third differential pair C+ andC− (433 a, 433 b) and fourth differential pair D+ and D− (434 a, 434 b)are connected by a second independent differential connection (2120 a,2120 b). Insulating layers (122 a, 122 b, 122 c, 122 d, 122 e) omittedfor clarity.

In view of the explanations set forth above, readers will recognize thatthe benefits of creating in-via routing with a light pipe according toembodiments of the present invention include: multiple independentconnections in a via without a second plating process or furthermechanical processing such as back-drilling, a simpler process for theconnection of non-adjacent wiring layers in a via, and a simpler processfor the connection of differential traces in a via.

Unless otherwise noted, like reference numerals in the description andvarious figures indicate like components, materials, steps, orprocesses.

Exemplary embodiments of the present invention are described largely inthe context of a fully functional computer system for creating in-viarouting with a light pipe. Readers of skill in the art will recognize,however, that the present invention also may be embodied in a computerprogram product disposed upon computer readable storage media for usewith any suitable data processing system. Such computer readable storagemedia may be any storage medium for machine-readable information,including magnetic media, optical media, or other suitable media.Examples of such media include magnetic disks in hard drives ordiskettes, compact disks for optical drives, magnetic tape, and othersas will occur to those of skill in the art. Persons skilled in the artwill immediately recognize that any computer system having suitableprogramming means will be capable of executing the steps of the methodof the invention as embodied in a computer program product. Personsskilled in the art will recognize also that, although some of theexemplary embodiments described in this specification are oriented tosoftware installed and executing on computer hardware, nevertheless,alternative embodiments implemented as firmware or as hardware are wellwithin the scope of the present invention.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A method of creating in-via routing with a lightpipe, the method comprising: applying a resist layer over a layer ofconductive material provided in a via of a printed circuit board;inserting the light pipe into the via, wherein the surface of the lightpipe includes at least one masked portion and at least one unmaskedportion; exposing a portion of the resist layer with light emitted fromthe at least one unmasked portion of the light pipe; and removing aportion of the conductive layer corresponding to the exposed portion ofthe resist layer.
 2. The method of claim 1 wherein applying a resistlayer over a layer of conductive material provided in a via includesproviding the via, wherein the via has been plated with the conductivematerial.
 3. The method of claim 1 wherein removing a portion of theconductive layer corresponding to the exposed portion of the resistlayer includes etching the via with acid.
 4. The method of claim 1wherein the resist layer is a positive photoresist material.
 5. Themethod of claim 1 wherein removing a portion of the conductive layercorresponding to the exposed portion of the resist layer includescreating at least two independent connections in the via.
 6. The methodof claim 1 wherein removing a portion of the conductive layercorresponding to the exposed portion of the resist layer includesremoving a conductive stub between a conductive pad on a surface of theprinted circuit board and a conductive trace in an interior layer of theprinted circuit board.
 7. The method of claim 1 wherein removing aportion of the conductive layer corresponding to the exposed portion ofthe resist layer includes removing partially removing conductivematerial between a first conductor in a first interior layer of theprinted circuit board and a second conductor in a second interior layerof the circuit board.
 8. A system for creating in-via routing with alight pipe, the apparatus comprising: a light pipe, wherein the surfaceof the light pipe includes at least one masked portion and at least oneunmasked portion; a light source; and a via of a printed circuit boardin which is disposed a layer of conductive material, wherein the systemis configured to carry out the steps of: applying a resist layer overthe layer of conductive material provided in the via, inserting thelight pipe into the via, exposing a portion of the resist layer withlight emitted from the at least one unmasked portion of the light pipe,and removing a portion of the conductive layer corresponding to theexposed portion of the resist layer.
 9. The system of claim 8 whereinapplying a resist layer over a layer of conductive material provided ina via includes providing the via, wherein the via has been plated withthe conductive material.
 10. The system of claim 8 wherein removing aportion of the conductive layer corresponding to the exposed portion ofthe resist layer includes etching the via with acid.
 11. The system ofclaim 8 wherein the resist layer is a positive photoresist material. 12.The system of claim 8 wherein removing a portion of the conductive layercorresponding to the exposed portion of the resist layer creating atleast two independent connections between in the via.
 13. The system ofclaim 8 wherein removing a portion of the conductive layer correspondingto the exposed portion of the resist layer includes removing aconductive stub between a conductive pad on a surface of the printedcircuit board and a conductive trace in an interior layer of the printedcircuit board.
 14. The system of claim wherein removing a portion of theconductive layer corresponding to the exposed portion of the resistlayer includes removing partially removing conductive material between afirst conductor in a first interior layer of the printed circuit boardand a second conductor in a second interior layer of the circuit board.15. A multilayer printed circuit board comprising: at least twoconductive traces; at least one insulator layer separating the at leasttwo conductive traces; and at least one via in a direction perpendicularto a plane of the printed circuit board that intersects the at least twoconductive traces, wherein the at least one via is configured within-via routing, wherein the in-via routing is form by: applying a resistlayer over a layer of conductive material provided in the via, insertingthe light pipe into the via, exposing a portion of the resist layer withlight emitted from the at least one unmasked portion of the light pipe,and removing a portion of the conductive layer corresponding to theexposed portion of the resist layer.
 16. The printed circuit board ofclaim 15 wherein applying a resist layer over a layer of conductivematerial provided in a via includes providing the via, wherein the viahas been plated with the conductive material.
 17. The printed circuitboard of claim 15 wherein removing a portion of the conductive layercorresponding to the exposed portion of the resist layer includesetching the via with acid.
 18. The printed circuit board of claim 15wherein the resist layer is a positive photoresist material.
 19. Theprinted circuit board of claim 15 wherein removing a portion of theconductive layer corresponding to the exposed portion of the resistlayer creating at least two independent connections between in the via.20. The printed circuit board of claim 15 wherein removing a portion ofthe conductive layer corresponding to the exposed portion of the resistlayer includes removing a conductive stub between a conductive pad on asurface of the printed circuit board and a conductive trace in aninterior layer of the printed circuit board.